1. Field of the Invention
The present invention relates to a furnace for the thermal treatment of charges of iron and steel components. The furnace includes a housing, a heating chamber disposed in the housing, and electrically energized heating elements that are disposed in the heating chamber for heating up the charge.
2. Description of the Prior Art
Furnaces for the thermal treatment of iron and steel components are known where heating-up of the charge is effected via heating elements that are disposed within the heating chamber and that are comprised either of graphite or, where greater thermal stress is encountered, of molybdenum. These heating elements are generally secured to the inner wall of the heating chamber, with the electrical connections for the heating elements extending through the wall of the heating chamber.
Furnaces embodied in this manner are predominantly operated as vacuum furnaces. In this connection, the furnace is evacuated for the duration of the process of heating up the charge. Thus, the charge is heated up nearly exclusively by heat radiated directly from the heating elements.
In order to provide for a controlled cooling of the charge, the heretofore known furnace is provided with a system for the supply of cooling gas; gas flows to the charge in a defined manner via a plurality of cooling gas openings in the heating chamber. A desired cooling of a specific portion or portions of the charge can in particular be undertaken by supplying only some of the cooling gas openings. Loading of the heretofore known furnace is effected in a vertical direction by delivering the base, which is loaded with the charge, to the furnace from below, as a result of which the charge enters the heating chamber.
Unfortunately, this heretofore known construction has the drawback that the rate of heating in the lower temperature range is very slow because the heat transfer via radiation tends to still be slow. Although convection can bring about considerable improvements in this temperature range, the air that circulates within the heating chamber requires a long period of time before it is heated up by the heating elements and can transfer this heat convectively to the charge. In addition, due to the small surface area of the heating elements, which are made of solid material, the radiation surface of the heating elements remains small. However, the magnitude of the radiation surface is proportional to the magnitude of the quantity of heat that can be radiated. Furthermore, due to their great thickness, the heating elements still radiate heat after energy is no longer supplied to the heating elements, thus delaying the beginning of the subsequent cooling phase.
It is therefore an object of the present invention to provide a furnace for the thermal treatment of iron and steel components that permits a rapid and uniform heating-up in every temperature range, that operates efficiently, and that permits a rapid reduction of temperature in the cooling phase.